Gel properties of collagens from skins of cod (Gadus morhua) and hake (Merluccius merluccius) and their modification by the coenhancers magnesium sulphate,glycerol and transglutaminase

The gel properties of two different kinds of fish gelatins prepared from cod (Gadus morhua) and hake (Merluccius merluccius) and modified by the coenhancers glycerol, salt and microbial transglutaminase, were examined. Gel strength was substantially increased by the addition of coenhancers although results varied, depending on the species. In gelatin from hake (M. merluccius) skin, the highest values were obtained with 10 mg/g of transglutaminase, whereas magnesium sulphate was more effective at both concentrations (0.1 and 0.5 M) in gelatin from cod (G. morhua) skin. Although, in both gelatins, the addition of any ingredient increased the viscosity modulus (G″), the elastic modulus (G′) was only increased by the addition of glycerol 15% (w/v) and MgSO₄ 0.5 M in hake (M. merluccius) gelatins; in cod (G. morhua) it was increased by all ingredients. The gelling and melting points, very important properties in fish gelatin, showed a notable improvement, the behaviour being different, depending on the species.     

Characterization of fish gelatin from surimi processing wastes: Thermal analysis and effect of transglutaminase on gel properties

Fish gelatin extraction from wastes of fish Herring species (Tenualosa ilisha) was carried out by a series of pretreatment with 0.2 M Ca(OH)₂ followed by 0.1 M citric acid and final water extraction at 50 °C for 3 h. The resulting fish gelatin preparation was evaluated for its dynamic viscoelastic properties, gelling and melting temperatures and gel strength. The gelling and melting temperatures of gelatin samples (at 6.67%, w/v) were obtained from differential scanning calorimetry and rheological studies. The melting temperature of extracted fish gelatin (EFG) obtained ranged from 16.2 to 16.7 °C compared to that of commercial fish gelatin gel (CFG), from 23.7 to 25.6 °C and halal bovine gelatin (HBG), from 26.5 to 28.7 °C. On the other hand, gelling temperatures of EFG, CFG and HBG ranged from 5.1 to 5.2 °C, 11.9 to 17.46 °C, and 12.6 to 19.33 °C, respectively. EFG gave gels with a considerably lower G′ values than CFG and HBG. The bloom strength of EFG gels at 6.67% (w/v) was 69.03 g which was much lower than HBG (336.2 g) and CFG (435.9 g). Enzyme transglutaminase was added in the amounts of 0.5, 1.0, 3.0 and 5.0 mg/g gelatin to modify the gel properties of the extracted fish gelatin. The modified EFG gels obtained had higher gel strengths of 101.1 g and 90.56 g with added transglutaminase of 1.0 and 3.0 mg/g, respectively. However with addition of 5.0 mg/g enzyme the gel strength increased only up to 75.06 g. SDS-PAGE of extracted gelatin gel showed protein band intensities for α1-chains and 53 kDa but in gels added with higher concentration of transglutaminase, these protein band intensities seemed to disappear.     

Comparison of gelling properties and flow behaviors of microbial transglutaminase (MTGase) and pectin modified fish gelatin

The gelling and structural properties of microbial transglutaminase (MTGase) and pectin modified fish gelatin were compared to investigate their performances on altering fish gelatin properties. Our results showed that within a certain concentration, both MTGase and pectin had positive effects on the gelation point, melting point, gel strength, textural, and swelling properties of fish gelatin. Particularly, low pectin content (0.5%, w/v) could give fish gelatin gels the highest values of gel strength, melting temperature, and hardness. Meantime, flow behavior results showed that both MTGase and pectin could increase fish gelatin viscosity without changing its fluid characteristic, but the latter gave fish gelatin higher viscosity. Both MTGase and pectin could increase the lightness of fish gelatin gels but decreases its transparency. More importantly, fluorescence and UV absorbance spectra, particle size distribution, and confocal microscopy results indicated that MTGase and pectin could change the structure of fish gelatin with the formation of large aggregates. Compared with MTGae modified fish gelatin, pectin could endow fish gelatin had similar gel strength, thermal and textural properties to pig skin gelatin.     

提取pH对鳙鱼鱼鳞明胶功能性质的影响

研究了制备过程中pH值(3.0~7.0)对鳙鱼鱼鳞明胶组成、得率和功能性质(凝胶强度、胶融温度和浊度)的影响,并对鱼鳞明胶的分子量分布进行了探究。结果表明,pH值在3.0~7.0时均能得到高品质的鱼鳞明胶(高蛋白质含量、低灰分含量)。随着pH值的增加,鳙鱼鱼鳞明胶得率逐渐降低,浊度逐渐增加,凝胶强度和胶融温度先增加后减小。此外,鳙鱼鱼鳞明胶的凝胶强度与分子量分布具有一定的相关性。上述研究结果可为特定用途的鱼明胶制备提供技术支撑。     

Effect of microbial transglutaminase on the functional properties of megrim (Lepidorhombus boscii) skin gelatin

This paper examines the effect of a microbial transglutaminase (TGase) on the gelling and viscoelastic properties of a gelatin from megrim (Lepidorhombus boscii) skins. Although TGase extended the setting time of fish gelatin, it was found that melting temperature, gel strength and viscosity in solution at 60 °C were considerably increased by the covalent cross‐linking action of the enzyme, as observed by SDS‐PAGE and SEM. Increasing concentrations of TGase increased the elasticity and cohesiveness of gelatin gels but reduced gel strength and hardness. Partial inactivation of the enzyme was achieved thermally without negatively affecting the properties of the gelatin; whether or not gelatin is thermoreversible depends essentially on the degree of enzyme inactivation. © 2001 Society of Chemical Industry     

Strength of Protein Gels Prepared with Microbial Transglutaminase as Related to Reaction Conditions

Influence of gelling reaction conditions on the strength of several protein gels prepared with microbial transglutaminase (TGase) was investigated. A method was developed to gel proteins and measure gel breaking strength in a micro well plate. Enzyme concentration range for maximum gel breaking strength varied from 10 to 40 units/g protein. Maxima gel breaking strengths were achieved at 50°C for SPI, caseinate and gelatin and 65°C for egg yolk and egg white proteins. Optimum pH resulting in strong gels was pH 9 for SPI, caseinate, and egg yolk, and pH 6 for gelatin and egg white. Adjusting pH was promoted in egg white the formation of ?-(γ-glutamyl)lysine crosslinks and increased its gel breaking strength.     

Repurposing fish waste into gelatin as a potential alternative for mammalian sources: A review

Mammalian gelatin is extensively utilized in the food industry because of its physicochemical properties. However, its usage is restricted and essentially prohibited for religious people. Fish gelatin is a promising alternative with no religious and social restrictions. The desirable properties of fish gelatin can be significantly improved by various methods, such as the addition of active compounds, enzymes, and natural crosslinking agents (e.g., plant phenolics and genipin), and nonthermal physical treatments (e.g., ionizing radiation and high pressure). The aim of this study was to explore whether the properties of fish gelatin (gel strength, melting or gelling temperature, odor, viscosity, sensory properties, film-forming ability, etc.) could be improved to make it comparable to mammalian gelatin. The structure and properties of gelatins obtained from mammalian and fish sources are summarized. Moreover, the modification methods used to ameliorate the properties of fish gelatin, including rheological (gelling temperature from 13–19°C to 23–25°C), physicochemical (gel strengths from ∼200 to 250 g), and thermal properties (melting points from ∼25 to 30°C), are comprehensively discussed. The relevant literature reviewed and the technological advancements in the industry can propel the development of fish gelatin as a potential alternative to mammalian gelatin, thereby expanding its competitive market share with increasing utility.     

Enhancement of Functional Properties of Wami Tilapia (Oreochromis urolepis hornorum) Skin Gelatin at Different pH Values

The effects of several agents in two different concentrations and pH values (5.0 and 8.0) on the functional properties of tilapia (Oreochromis urolepis hornorum) skin gelatin were evaluated and compared using a control tilapia skin gelatin and a commercial mammalian gelatin. The addition of the agents (sucrose 4 % and 8 % (w/v), glycerol 5 % and 10 % (v/v), NaCl 0.3 and 0.8 mol/L, MgCl₂ 0.3 and 0.8 mol/L, MgSO₄ 0.3 and 0.8 mol/L, KCl 0.3 and 0.8 mol/L, and transglutaminase 10 and 15 mg/mL) slightly increased the turbidity. There were different ratios of rheological properties depending on the agent, concentration, and pH. The addition of all agents increased the viscosity of the gelatin solution, mainly at pH 5.0. The addition of glycerol (10 % (v/v)) raised viscosity up to 7.45 cP. The setting time was prolonged by incorporating the agents. The gelatin samples with the addition of MgSO4 0.8 mol/L showed higher gel strength than the mammalian gelatin, exhibiting values of 298 and 295g_f at pH 5.0 and 8.0, respectively.     

African catfish (Clarias gariepinus) skin gelatin: Extraction optimization and physical–chemical properties

Large amounts of by-products are generated in fish processing. It is estimated that the residues from filleting can represent up to 75% of the total weight, and that approximately 30% of such residues consist of skin and bones. There is currently an increased interest in fish gelatin. This work investigated the variables of the extraction process that can potentially influence the gelatin properties of catfish skin and its physicochemical characteristics. The screening step determined the extraction temperature °C, extraction time h, and H₂SO₄% p/v concentration, which were selected to assemble a central composite rotational design (CCRD) in order to elucidate its effect on gelatin viscosity (p < 0.05). The viscosities of the African catfish skin gelatin were between 2.05 and 2.85 mPa·s. The extraction process exhibited a yield of 11.4% and gelatin gel strength and melting point was of 234 g and 25.7 °C, respectively.     

鱼鳞明胶的提胶工艺

根据单因素试验结果,利用正交试验,考察了提胶温度、pH值和时间对鱼鳞明胶品质的影响。并得到提胶条件为:提胶温度为55℃,pH值为6,时间为5h。在该条件下明胶的提取率达到58%,6.67%的明胶溶液在60℃时的黏度为8.16mPa·s,7℃下保温18h后凝胶强度为1 202.65g,约290Bloom,凝胶温度和熔化温度分别为20.8℃,26.9℃,等电点约为pH 7,可达到高品质明胶的要求。     

Visco‐Elastic and Flow Properties of Gelatin from the Bone of Freshwater Fish (Cirrhinus mrigala)

The average yield of gelatin from the bone of freshwater fish (Cirrhinus mrigala) was 6.13%. The fluorescence spectra revealed maximum emission at 303 nm indicating the exposure of chromophores to bulk solvent. The amino acid profile of gelatin revealed a higher proportion of glycine and imino acids. The bloom strength of gelled gelatin was 159.8 g. The average molecular weight of fish bone gelatin was 281 kDa as determined by gel filtration technique. The dynamic oscillatory test of gelatin solution as a function of time and temperature revealed gelling and melting temperatures of 8.0 °C and 17.0 °C, respectively. The flow behavior of gelatin solution as a function of concentrations and temperatures revealed non‐Newtonian behavior with pseudo‐plastic phenomenon. The Herschel–Bulkley and Casson models were found suitable to study the flow behavior. The emulsion capacity (EC) of gelatin was inversely proportional to its concentration.     

Improving the physical properties of fish gelatin by high hydrostatic pressure (HHP) and ultrasonication (US)

In this study, it was aimed to improve the physical properties of fish gelatin by using high hydrostatic pressure (HHP) and ultrasonication (US). Gelatin solutions were exposed to different pressures and ultrasonication separately and gelled afterwards. The physicochemical measurements based on gel strength, turbidity and rheology experiments showed that HHP treatment on fish and bovine gelatin stabilized the gelatin network by organising the structure and reducing the free volume. Both processing methods (HHP and US) increased the gel strength significantly (P < 0.05) compared with non-treated samples. Fourier-transform infrared spectroscopy (FTIR) results indicated that conformations of amino acids changed after the treatments. Furthermore, US treatment was shown to destroy the gelatin network, change the gelation mechanism and decreased the degree of aggregation. Both treatments improved the gel characteristics as gel strength, gelling and melting temperatures of the fish gelatin. At the end, the best combination for fish gelatin among HHP and US treatments was found as 400 MPa–10 °C–15 min pressurisation.     

Characterization of gelation time and texture of gelatin and gelatin–polysaccharide mixed gels

The effects of cooling rate, holding temperature, pH and polysaccharide concentration on gelation characteristics of gelatin and gelatin–polysaccharide mixtures were investigated using a mechanical rheometer which monitored the evolution of G′ and G″. At low holding temperatures of 0 and 4 °C, elastic gelatin gels were formed whereas a higher holding temperature of 10 °C produced less elastic gels. At slow cooling rates of 1 and 2 °C/min, gelling was observed during the cooling phase in which the temperature was decreased from room temperature to the holding temperature. On the other hand, at higher cooling rates of 4 and 8 °C/min, no gelation was observed during the cooling phase. Good gelling behavior similar to that of commercial Strawberry Jell-O^® Gelatin Dessert was observed for mixtures of 1.5 and 15 g sucrose in 100 ml 0.01 M citrate buffer containing 0.0029–0.0066 g low-acyl gellan. Also, these mixed gels were stronger than Strawberry Jell-O^® Gelatin Desserts as evidenced by higher G′ and gel strength values. At a very low gellan content of 0.0029 g, increasing pH from 4.2 to 4.4 led to a decrease in the temperature at the onset of gelation, G′ at the end of cooling, holding and melting as well as an increase in gel strength. The gelation time was found to decrease to about 40 min for gelatin/sucrose dispersions in the presence of 0.0029 g gellan at pH 4.2 whereas the corresponding time at pH 4.4 was higher (79 min). In general, the gelation time of gelatin/sucrose dispersions decreased by a factor of 2 to 3 in the presence of low-acyl gellan. The addition of low-acyl gellan resulted in an increase in the gelation rate constant from 157.4 to 291 Pa. There was an optimum low-acyl gellan content for minimum gelation time, this optimum being pH dependent. Addition of guar gum also led to a decrease in gelation time to 73 min with a corresponding increase in the gelation rate constant to 211 Pa/min though these values were not sensitive to guar gum content in the range of 0.008–0.05 g. The melting temperature of gelatin/sucrose/gellan as well as gelatin/sucrose/guar mixtures did not differ significantly from that of pure gelatin or Strawberry Jell-O^® Gelatin Desserts. At pH 4.2, the melting rate constant was highest at a low-acyl gellan content of 0.0029 g whereas the rate constant was insensitive to low-acyl gellan content at pH 4.4. Addition of guar did not seem to affect the melting temperature or the melting rate constant.     

鱼鳞明胶与哺乳动物明胶性质的比较

研究了酶法制备的草鱼鱼鳞明胶的理化性质,并将其与哺乳动物明胶的性质作了比较。研究发现,草鱼鱼鳞明胶中富含甘氨酸、脯氨酸、羟脯氨酸和丙氨酸,而亚氨基酸、总疏水性氨基酸的含量以及平均疏水性值要小于哺乳动物明胶;分子质量分布主要以α组分和β组分为主,占明胶分子总量的88%;胶凝温度和熔化温度分别为20.8℃和26.9℃,低于哺乳动物明胶;特性黏度约为0.73;表面疏水性指数为259.59,有较好的乳化性和起泡性。此外发现,明胶的高凝胶强度和胶凝速度主要取决于明胶(α+β)组分的含量,而明胶胶凝和熔化温度则主要取决于亚氨基酸的含量,不同来源明胶的特性黏度η仅与其α组分(α1+α2)的含量存在线性相关。     

Effect of EDTA, HCl, and Citric Acid on Ca Salt Removal from Asian (Silver) Carp Scales Prior to Gelatin Extraction

ABSTRACT:  Pretreatments with different chemicals at different concentrations to remove Ca compounds were studied to determine their effects on gelatin extraction from silver carp ( Hypophthalmichthys molitrix ) scales. During Ca removal with HCl, citric acid, and EDTA, all 3 chemicals were able to decalcify (>90%) scales; however, protein losses with EDTA were lower than with HCl and citric acid ( P  < 0.05), and protein losses with citric acid were lower than with HCl ( P  < 0.05). Ca removal with HCl yielded a solution where 4% to 5% of the protein was Hyp, with estimated gelatin losses from 0.9% to 2.5%. After 0.20 mol/L HCl was used for Ca removal, the extracted gelatin solution was 15.4% of the initial scales weight and gave a gel strength of 128 g. After using 1.2 g/L citric acid for Ca removal, the extracted gelatin solution was only 9% of the scales and the gel strength was 97 g. Using 0.20 mol/L EDTA for Ca removal gave a yield of 22% and a gel strength of 152 g. These data suggest that EDTA at 0.20 mol/L provides the best Ca removal with minimal collagen/gelatin removal (estimated gelatin loss was less than 0.013%) during the Ca removal step, and subsequently gave a high gelatin yield and gel strength. Fish gelatin has generally been extracted from fish skins and occasionally fish bones. This article focuses on removing the Ca compounds in fish scales and then producing fish gelatin with a good gel strength and yield. With further studies, this study may help the fish industry to have a new source of fish gelatin for food and pharmaceutical applications.     

Characterizations of fish gelatin films added with gellan and κ-carrageenan

Fish gelatin is known to be inferior to mammalian gelatins. Gellan and κ-carrageenan were added to improve properties of the fish gelatin films. Initially, polysaccharides were added to make fish gelatin gels, and tested for the melting point. Mechanical, barrier, color and microstructure properties, as well as Fourier transform infrared (FTIR) and thermal analysis (DSC) of the modified fish gelatin films were evaluated. The addition of gellan and κ-carrageenan increased the melting point of fish gelatin gels, gellan being more effective. Polysaccharides modified fish gelatin films by increasing tensile strength and barrier against water vapor, but made films slightly darker. Scanning electron microscopy (SEM) microstructure analysis revealed that gellan eliminated cracks present in the film matrix resulting in a more uniform structure. FTIR and DSC analyses showed that both polysaccharides effectively interacted with fish gelatin, and moreover, gellan being more effective. Overall, addition of gellan up to 2 g/100 g of gelatin performed better in enhancing fish gelatin films properties.     

Yield,viscosity, and gel strength of wami tilapia (Oreochromis urolepis hornorum) skin gelatin: Optimization of the extraction process

A factorial design and response surface methodology were used to optimize the extraction process of tilapia skin gelatin (Oreochromis urolepis hornorum). The concentrations of NaOH (0.15%–0.35%) and H₂SO₄ (0.15%–0.35%), the extraction temperature (40°C–60°C), and the extraction time (3–15 h) were independent variables. Response variables were yield (%), viscosity (mPa·s), and gel strength (g). The NaOH (%) and H₂SO₄ (%) concentrations had significant influences (p<0.05) on viscosity and gel strength, while the extraction temperature (°C) and the extraction time (h) showed significant influences (p<0.05) on all dependent variables. Increasing the temperature and extraction time provided higher yields with a reduction in the gelatin viscosity and gel strength. Tilapia fish skin can be used as a source for production of gelatin.     

响应曲面法优化苜蓿成冻特性研究

采用响应曲面法(RSM)研究了明胶、魔芋胶和蔗糖酯用量对苜蓿成冻特性的影响。建立苜蓿成冻的二次多项数学模型,并验证模型的有效性,得出优化的工艺条件为：明胶用量3.00%,魔芋胶用量3.00%,蔗糖酯用量2.93%,在此条件下,苜蓿冻的硬度为4477g,黏着性为－ 6456g,内聚性为0.3127,胶着性为1408g,咀嚼性为1388g。     

Characteristics and chemical composition of skins gelatin from cobia (Rachycentron canadum)

Gelatin was obtained from cobia (Rachycentron canadum) skins, which is an important commercial species for marine fish aquaculture, and it was compared with gelatin from croaker (Micropogonias furnieri) skins, using the same extraction methodology (alkaline/acid pre-treatments). Cobia skins gelatin showed values of protein yield, gelatin yield, gel strength, melting point, gelling point and viscosity higher than the values found from croaker skins gelatin. The values of turbidity and Hue angle for cobia and croaker gelatins were 403 and 74 NTU, and 84.8° and 87.3°, respectively. Spectra in the infrared region had the major absorption band in the amide region for both gelatins, but it showed some differences in the spectra. The proline and hydroxyproline contents from cobia skins gelatin (205 residues/1000 residues) was higher than from croaker skins gelatin (188 residues/1000 residues). SDS-PAGE of both gelatins showed a similar molecular weight distribution to that of standard collagen type I. Therefore, cobia skins could be used as a potential marine source of gelatin obtainment for application in diversified industrial fields.